This is a competitive renewal of NIH grant DK31036 which is focused on the insulin receptor and alterationsin its expression and/or function in physiologicand pathologic states. During the past 5 years, we have identified one of the enzymes involved in processing of the pro-insulin receptor, studied the role of compartmentalization in insulin signaling;studied the structure/function relationshipsbetween the IGF-1 and its receptor using a novel application of the yeast two-hybrid system;used homologous recombination to create knockout models of Type 2 diabetes;and developed and used the system of tissue-specific knockout technology (Cre-/ox) to determine the role of individual tissues in the physiology of glucose homeostasis and the pathophysiology of diabetes, focusing on skeletal muscle and pancreatic P- cells. In the coming grant period, we will continuedissection of the pathophysiology of diabetes using the insulin and the IGF-1 receptors as a target and a tool. Specifically,we propose to: 1)Create, characterize and further analyze tissue- specific knockouts of the insulin receptor in classic target tissues for insulin action (liver, muscle and fat) and non- classical target tissues (P-cell,brain, vascularendothelialcells, and smooth muscle cells) using the Cre-Lox system. The analysis of these will includedetermining the role of insulin signaling in each of these cell types, the pathophysiological effects of the tissue-specific insulin resistance, the nature of compensatory responses in other tissues, analysis of the role of insulin receptors in insulin clearance, and in a few cases, creation of double tissue specific knockouts. 2) Compare and contrast the role of insulin and IGF-1 receptors by creating and characterizing p-cell and muscle specific IGF-1 receptor knockout mice to compare the insulin receptor knockouts in these tissues. We will also create double knockouts of the insulin and IGF-1 receptors in these tissues to determine the role of each receptor in compensation for the other. 3) Define endogenous genes of the mouse which contribute to or modify insulin resistance and the diabetic phenotype in knockout mice by analysis of the genetics of the insulin receptor/IRS-1 double heterozygote knockout mouse on different genetic backgrounds. 4) Analyze gene expression in tissues lacking functional insulin receptors to define differences in direct and indirect regulation by insulin and metabolic substrates in this class of insulin actions.